电极材料对低密度聚乙烯中空间电荷的影响

用电声脉冲法(PEA)测量了不同电极材料对低密度聚乙烯(LDPE)中空间电荷的影响。电极材料为常见的金属,如:铝、含铅黄铜、含锌黄铜和紫铜。实验发现不同电极材料均有空穴和电子注入;并且在实验条件下电极功函数越高越容易注入空穴,功函数越低越容易注入电子;铝(+)/紫铜(-)电极系统能有效减少聚乙烯中的空间电荷注入,进而抑制因空间电荷聚集引起的局部场强过高。     

交流电压下聚合物绝缘材料电致发光特性

设计了绝缘材料电致发光现象研究所用的实验装置,以低密度聚乙烯(LDPE)、聚丙烯(PP)和聚四氟乙烯(PTFE)三种聚合物绝缘材料为样品,研究了交流电压下聚合物材料表面电致发光的时域和相域特性,同时探讨了不同电极材料(铜、铝)以及在材料表面溅射金膜电极对聚合物表面电致发光现象的影响.实验结果显示,不同聚合物材料的电致发光起始电压和发光强度各不相同,但有相似的时域和相域特性曲线,阶升/降电压下的发光曲线均表现出类似于磁滞回线的现象;同时发现不同电极材料下以及溅射金膜电极后的材料的电致发光也表现出不同的发光起始电压和强度.认为电极与材料的接触势垒和材料内部空间电荷影响着材料的电致发光特性.     

半导电材料对纳米MgO/XLPE复合介质空间电荷影响的研究

聚合物纳米复合介质中空间电荷的注入与半导电电极材料密切相关,文中采用电声脉冲(PEA)法测量了预压-60 kV/mm电场1 h后,对比研究了六种不同半导电电极材料下交联聚乙烯(XLPE)和MgO/XLPE复合介质中的空间电荷分布;并对不同半导电电极材料下MgO/XLPE复合介质中的平均电荷密度进行了计算。对比实验表明:配方不同的半导电电极材料确实对试样中空间电荷的分布以及空间电荷量影响很大;以乙烯醋酸乙烯共聚物(EVA)为基础材料、添加30wt%炭黑的第二种半导电材料对MgO/XLPE复合介质中空间电荷的抑制效果最好。     

双极性脉冲激励的填充式介质阻挡放电反应器结构和电气参数优化

该文利用双极性脉冲电源激励填充床反应器。为了优化填充式介质阻挡放电反应器结构和电气参数,研究了不同电极形状、电极直径、石英管管径、填充材料(玻璃珠)粒径、脉冲成形电容等参数对反应器放电功率的影响。实验结果表明,采用螺纹棒电极的反应器放电功率高于普通棒状电极,增大电极直径或减小外部石英管的管径均能显著增加反应器的注入功率,填充玻璃珠的粒径越小越有利于反应器的能量注入。相同电压下,当脉冲成形电容从0.5增至1.5 n F,反应器的注入功率和放电电流增幅较大;当成形电容值大于1.5 n F时,反应器注入的功率和电流并没有显著提高。因此,1.5 n F是优化过的最佳脉冲成形电容值,是反应器静态电容(75 p F)的20倍。     

聚乙烯与聚丙烯中空间电荷注入特性的比较

为研究聚乙烯与聚丙烯中空间电荷注入特性,比较不同电极材料对空间电荷注入特性的影响,使用激光诱导压力波法研究了不同电极材料下2种试样中空间电荷注入及迁移情况,电极选取的是掺有碳黑的乙烯与乙酸乙烯共聚物半导电电极和铝电极。试验结果表明:在使用半导电电极的情况下聚乙烯及聚丙烯试样均有空间电荷的注入与迁移,其中聚乙烯试样中载流子的迁移率要明显高于聚丙烯试样;对于蒸镀有铝电极的2种试样则空间电荷注入明显减少;2种试样在不同电极情况下载流子在阴极的注入量均要大于阳极处的注入量。针对上述现象该研究从能带理论出发给出了相应解释:试样材料电子亲和力越高越容易注入电子;电场作用下材料能带的倾斜造成了载流子注入量在阴极和阳极处的差异;试样中载流子迁移率的差别则是因为材料内部陷阱数与深度的不同造成的。     

加聚酰亚胺薄膜阻挡层的聚乙烯中空间电荷分布特性的研究

选用聚酰亚胺(PI)薄膜作为电极注入的阻挡层,用电声脉冲法装置测量茂金属聚乙烯(MPE)试样中空间电荷的分布。试验结果表明:在高场强下,放置在上电极和MPE之间的阻挡层,既能有效地抑制负电极的电子的注入,也能阻止正电极的空穴注入到MPE。用聚合物的能带和界面理论解释了实验现象。     

现场椭偏术研究钴离子注入对碱性镍电极的影响

为了提高镍电极表面活性物质的利用率和深入认识镍电极的性能,应用光谱电化学研究方法——椭圆偏振光现场测试技术研究了碱性溶液中镍电极的性质.讨论了充电电流与放电电流以及钻离子注入对碱性镍电极性能的影响.实验结果表明:在表面层中注入钴离子后,可以改良在碱性镍电极表面形成活性物质层的均匀性,形成较厚的表面活性物质层,提高碱性镍电极表面氧化层的钝化性能,若对碱性镍电极施以较大的阳极极化电流,表面上注入的钴离子能够在充电过程中使更多的Ni(OH)_2转化到NiOOH,从而提高了碱性镍电极的容量.文中还介绍了椭圆偏振技术应用于现场电极反应研究的优越性.     

非晶纳米氢氧化镍电极材料的研究

介绍了非晶纳米Ni(OH)2材料的制备方法以及用XRD、TEM和SAD3种方法研究了这种电极材料的结构特性;报导了非晶纳米Ni(OH)2电极的制备方法及其电化学性能测试方法。实验结果表明,非晶纳米Ni(OH)2电极具有容量大、放电电压高等优点,是一种高效的电极材料。     

基于Kerr电光效应测量的液体空间电荷产生及其分布特性

空间电荷是影响绝缘介质耐电强度,导致电场分布畸变和电介质击穿的重要参数之一。为了更深入地开展液体中空间电荷产生及其分布特性的试验及相关机理研究,采用基于Kerr效应的空间电荷高速CCD(charge-coupled device)测量系统,实现了碳酸丙烯酯中黄铜、不锈钢、铝3种电极材料在冲击电压下光强分布特性的测量;结合改进的图像处理技术,对极间电场随时间变化的动态发展过程进行反算;同时依据传统电击穿理论和双电层理论对空间电荷产生及发展的微观机理进行分析。研究表明:在不同材料以及不同电压极性下,空间电荷分布呈现出双极注入、正电荷注入及负电荷注入3种显著的注入特征,其中双极注入提高了液体电介质的冲击绝缘性能,正电荷注入和负电荷注入使得液体电介质绝缘性能降低,其注入特性的差异与外加电压大小、电极材料、电极表面状态等因素有关。     

RunMn1-nOx复合电极材料的制备、结构与电化学电容特性

为了提高钌基复合电极材料的性价比,首次采用氧化共沉淀法制备出RunMn1-nOx新型电化学电容器复合电极材料。X射线光电子能谱(XPS)分析表明该复合材料由氧化钌-二氧化锰组成。X射线衍射实验显示材料的晶态结构与热处理温度有关,且温度对材料的电化学电容性有影响。循环伏安(CV)以及计时电位测试结果表明RunMn1-nOx复合电极材料比纯MnO2电极材料具有更好电化学电容性和导电性,掺杂9%(质量分数)的钌可显著地提高金属氧化物复合电极材料的性价比。     

Space charge characterization in aged LDPE amalgamated insulationregions from underwater telecommunication systems

The requirement of insertion of optical amplifier units and joints, into long-distance submarine telecommunication systems, results in regions of the polymeric insulation which have to be reinstated, using injection molding techniques. These techniques introduce internal amalgamated interfaces, which subsequently can be the sites of possible electrical insulation failure in the system. This paper reports on space charge measurements, (using the pulsed electroacoustic (PEA) technique), from microtomed thin film samples taken from the interface region of typical system joints which have undergone accelerated aging tests under a dc voltage at room temperature. The space charge distributions obtained for the samples are discussed with reference to the underlying mechanisms of both the bulk low-density polyethylene (LDPE) and the surface (LDPE/electrode interface). The effect of varying the electrode material (i.e. Au and Al) is discussed with reference to previously published data. Finally the effects of long-term aging on space charge accumulation within LDPE are considered briefly     

High repetition rate PEA system for in-situ space charge measurement during breakdown tests

In order to investigate transient space charge phenomena, it is essential that the space charge profile be observed at a high repetition rate. We have developed a new space charge measurement system using the pulsed electroacoustic (PEA) method, which can measure the space charge profiles every 10 /spl mu/s. It employs the most recent digitising oscilloscope model and a semiconductor switch. The effect of prestressing on impulse breakdown voltage of a low-density polyethylene sheet was investigated by using the new system. Experimental results suggest that positive charge injection was dominant immediately before the breakdown, and charge injection during the prestressing causes distortion of the electric field near the electrode, and enhances the subsequent charge injection due to the impulse voltage.     

Dynamics of voltage polarity reversal as the controlling factor inspace-charge induced breakdown of insulating polymers

Our investigation is focused on the understanding of high-field phenomena in polymers. In highly insulating materials such as polyethylene, space charge has a strong influence on both the short and long term breakdown strengths. The aim of this report is to demonstrate and discuss the importance of the dynamics of voltage polarity reversal at the injecting needle electrode on space charge induced breakdown. Evidence of space charge injection is provided by the observation of local breakdown generated by grounding of the sample after the polarization (so-called `grounding' tree). The effect which is polarity dependent, can be observed only when the sample is short-circuited immediately after charging. Field computation is performed versus injected charge and a critical charge density is derived in order to explain polymer breakdown upon grounding. The time dependence of the effect is explained by space charge relaxation. Polymer degradation under ac voltage is discussed on the basis of this interpretation     

Computation methods for one-dimensional bipolar charge injection

Kerr electrooptic field-mapping measurements have shown strong space charge effects in high-voltage stressed dielectrics, where the magnitude and sign of injected charge depends on electrode material. With appropriate choice of electrode material combinations and voltage polarity is possible to have uncharged, unipolar positively or negatively charged, or bipolar charged dielectrics. The bipolar homocharge case lowers the electric field at both electrodes due to space-charge shielding, and thus allows a higher voltage without breakdown. Using charge-transport analysis the authors consider the general case of charge injection from both electrodes and solve time and space dependences of the electric field and charge distributions and the time dependences of the terminal voltage and current. This analysis extends earlier work by including nonequilibrium charge dissociation and recombination so that the effective ohmic conductivity is not constant but varies with time and position due to local net charge density. Specific cases discussed are the open-circuit voltage decay of an initially charged capacitor, the charging and discharging by a Marx generator, and alternating voltage excitations     

基于脉冲电声法的同轴塑料电缆空间电荷测量技术的研究进展

空间电荷现象严重制约着高压直流塑料电缆的发展。目前,脉冲电声法（pulse electric acoustic,PEA）是国际上常用的测量固体电介质中空间电荷分布的非破坏性的方法之一。首先从高压脉冲的注入方式出发,简述了几种基于PEA法的同轴塑料电缆空间电荷测量技术;同时,提出了一种基于高压脉冲从测量电极注入电缆试样的改进测量装置,在该装置中通过蓄电池、环氧底座以及光电转换器等将采集数据的示波器进行对地隔离,从而提高了测量系统测量信号的频带宽度;然后,介绍了同轴塑料电缆空间电荷波形的恢复方法;最后,概述了空间电荷测量技术在评估电力电缆老化程度中的应用和未来在线测量空间电荷的可行性及发展方向。     

Time-resolved space charge and electroluminescence measurements in polyethylene under ac stress

Time-resolved space charge (SC) and electroluminescence (EL) measurements are carried out on polyethylene films stressed under ac voltage at industrial frequency to probe injection, trapping and recombination of charge. SC is measured by pulsed electro-acoustic (PEA) technique at each zero voltage cross-over point of the ac voltage, thereby getting rid of the capacitive charge. EL is detected using photon counting techniques with a time resolution down to 50 /spl mu/s. Both SC and EL exhibit a threshold response as a function of the applied voltage. Numerical values of these thresholds are in good correspondence for SC and EL measurements in every tested material. Observations are consistent with a model of bipolar injection with an unbalanced situation in positive and negative charge behavior. It is also shown that different polyethylene materials behave differently relative to the field above which the charge is detected, providing thereby a way to compare the space charge behavior of those materials under ac field.     

硅橡胶中空间电荷的形成机理

文中采用电声脉冲法，在不同的直流电场作用下，测量了硅橡胶中空间电荷的分布，并分析了其与加压时间的关系。同时测量了短路电极时空间电荷分布的变化，讨论了电极短路试样中残留电荷的分布及其影响。研究发现，在场强相对较低(5kV／mm)与较高(60kV／mm，70kV／mm)时，电极附近介质中的电荷分布均为异极性电荷，但其形成机理完全不同；而在中场强(10kV／mm，30kV／mm)下可出现同极性电荷。文章还讨论了Al和Cu电极在不同电场强度下的电子或空穴注入现象以及其在空间电荷形成中的作用。     

Space charge formation and breakdown in polyethylene influenced by the interface with semiconducting electrodes

This paper deals with the influence of interface between polyethylene and semiconducting electrode on the space charge formation and electrical breakdown. Low‐density polyethylene (LDPE) films attached with different semiconducting electrodes were subjected to the DC breakdown test, and corresponding space charge distribution was measured. A heat treatment to LDPE itself did not bring about a significant change in space charge profile; however, when a semiconducting electrode was hot‐pressed, the impurities would migrate into LDPE at high temperature, leading to the change in space charge profile. Furthermore, it was suggested from the comparison between the results with degassed and as‐received semiconducting electrodes that some carriers relating to impurities in the electrode would move into LDPE under the voltage. In addition, it was shown that the breakdown is not determined by the field at the cathode which can supply sufficient electrons, but by the maximum field across the specimen, suggesting that an increase in conduction current due to the generation and/or injection, rather than the electronic avalanche process, leads to the breakdown. © 2001 Scripta Technica, Electr Eng Jpn, 138(3): 19–25, 2002     

Some factors for the space charge formation in polyethylene

Information on space-charge behavior in thick insulated samples aids in understanding the dc characteristics of polymer-insulated dc cables. The pulsed electroacoustic method is used to investigate several space charge formation factors in 2 mm-thick polyethylene (PE). The following results were obtained. For measurement factors: (1) A polymeric semiconducting electrode provides a more accurate measurement than does a metal electrode as a result of better matching of acoustic impedance with PE. (2) Within a dc electrical stress range of several tens kV/mm, the space charge distributions under and after dc voltage application are almost the same; this is due to a comparatively long time of space-charge decay. (3) The space-charge distribution of a plate sample agrees with that of a cable sample having the same insulation thickness. For insulating material factors: (1) The amount of space charge in crosslinked polyethylene (XLPE) is much larger than that in low-density PE (base of XLPE). The space charge of XLPE continues to increase even after dc voltage application (24 h); that of LDPE reaches equilibrium with a few hours. (2) The aforementioned space charge difference between XLPE and LDPE is assumed to be caused by ionic impurities in XLPE, not by the additives themselves (acetophenon and cumylalcohol as byproducts of cross linking and antioxidant).